We here on the El Reg gun sensation desk considered getting Gaz to make an unimportant part or accessory for his Lee Enfield out of 3D printed plastic, or in some other fashion involve a computer, which would probably have led to excited writeups in the world's media about Brit GUN NUT 3D PRINTS working SNIPER RIFLE in SHED, …

CR324

Scrap metal?

He cleaned up a working but dirty (very slightly rusty) receiver and trigger assembly, had a store-bought barrel attached and tested by a professional gunsmith, and bought a ready-made new wooden stock for it.

That's a fun wood-shop project, not "building a sniper rifle from scrap metal".

Re: Scrap metal?

Agreed, a fine bit of metal destined for the smelter was salvaged into a fine work of art. The veracity of it being a sniper rifle will be determined at the range.

To the author, you have a hunting season to take it to the range and improve your group to minute of angle with handloads. Two minutes of angle is acceptable for a service rifle but sniper rifles have a higher standard.

Edit: I take it back; assuming iron sights you're right on. I'd love to see the results with proper telescopic or laser sights.

Re: Scrap metal?

I've built a car before. Sure a lot of the parts; engine, transmission, uprights, rack, column, brakes, etc. were from the scrap yard, but the chassis and suspension components were home built from steel tube and plate.

The two problems with your title:

Scrap metal - scrap metal is unusable junk. The metal in this case was salvageable or perfectly usable second hand parts.

Built - Nope assembled from parts. To say you "built" a machine to me means you actually fabricated significant parts or at least did some serious work in making those parts fit. Assembly - sticking stuff together that was intended to go together. Building - fabrication or at least serious adaptation.

So "Brit GUN NUT assembled WORKING SNIPER RIFLE at home out of spare parts." FIFY.

Re: Scrap metal?

No, scrap metal is metal going for scrap. It can be perfectly useable but no longer useful - like the old cast iron radiators we used to scrap all the time when I was a builder. They worked. They didn't work well, so they were scrapped. That made them scrap metal, even though they were fully functional.

Re: Scrap metal? @ Grease Monkey

Built - Nope assembled from parts. To say you "built" a machine to me means you actually fabricated significant parts or at least did some serious work in making those parts fit. Assembly - sticking stuff together that was intended to go together. Building - fabrication or at least serious adaptation.

You mean like where the writer talks about doing serious fettling and so on to get things to fit? :) Sure, it is largely assembled, but he did resort to hand-tools to re-shape stock materials.

As to the scrap.. As a former metal finisher, and previously a worker in a foundary and other related parts of that factory, and also time in a few other places where engineering skills (including various metal working skills that would put my metalwork teachers to shame) were required - and with a few "significantly repaired" cars and complete bike rebuilds behind me, I add my vote to those saying "it's scrap". In farming, a weed is "an unwanted plant". A rose is a weed if it's not wanted in that area, as is cabbage or tulips or whatever. Much the same for for metal.

A friend of mine got a new never-used stainless sink and benchtop a few years back for the price of the scrap metal (and a little extra - had to be nice). Perfectly functional, hours spent making it, beautifully done, and it was scrap. Because the builder gave the wrong dimensions, so the maker put it out for scrap. I brought it and friends of his built a bench to suit. It's not scrap now, but if I hadn't been there at the right time to see it being loaded on the scrap truck (and had a friend needed some kitchen improvements), it would've been melted down shortly afterwards.

Re: Scrap metal?

Yes. Artisan gunsmiths in Afghanistan can and do build AK47's from scratch. Imports and salvaged guns fetch better prices, but there are perfectly usable and completely home-made AK47's for sale there.

Re: You did vary your certificate...

Re: You did vary your certificate...

Curious how painful the paperwork was. Assuming from the bootnote the receiver was with the RFD until you'd completed the rifle and transferred it to your ticket? I'm guessing that would be less complicated than trying to build & proof it on your own FAC. But congrats, and now you just have to resist upgrading it :p

Dirty gun porn!

Agree and agree

First, I agree that the headline made me think he was melting down soup cans and railroad track to cast pieces for a gun. The title was more exciting than the article.

The actual effort was a noble work of restoration. Regrettably, such efforts, reported accurately, are remarkably dull and boring. Scrape this. Cover this rusty area with oil and rub with a coarse rag until it's shiny. Make this fit. When it doesn't fit, take it apart, do something to it, and try again. Repeat. Then do something else that has to be done that will similarly test your commitment to finish the project. Try to keep your emotions under control so parts being manipulated don't suddenly take flight across the shop.

My Ford Model T came to me from various sources in quantities of rusty pieces that had to be disassembled, cleaned, and fit together again. That your rifle came out functioning at 3 minutes of dispersion--and feeding from the magazine on top of that--reflects well on your attention to detail. I would bet you learned a great deal, in addition to developing quantities of patience.

Nice job.

A surprising source for many ex-British WW2 small arms in good nick is Israel, which used a hodge-podge of European and American weaponry for many years. Wartime issue revolvers, rifles and parts often turn up on US dealers' websites, some not having been released from the Israeli reserve stocks until the late Eighties. They usually have a Star of David marking added to the standard British markings and have usually been well maintained. A common source of bad furniture, as I suspect the author stumbled on, is India. Whilst they used to make good parts at the factory in Ishapore, they also had a habit of selling on even parts that failed proof testing and these have also turned up on websites. Buying parts from eBay is not something I would recommend.

Re: Meh.

Oh, agreed - the real work was done by the gunsmith, who fabricated a thin bushing to get the barrel to time correctly, and headspacing it with a big tray of bolt heads and a set of go/no go gauges.

Mind you, given the space available there wasn't time to write about setting up the sights (ever tried to do that when the rearsight isn't true? Damn that axis pin - might have been bent as well as peened), the weeks of patient work it took to bed the thing properly, and my Heath Robinson solution to correcting the offset zero.

3MOA - worth bearing in mind factory reject standard for the No.4 was 4MOA. In addition, the bedding on this one could be a lot better and the barrel's an all-but-shot-out 1955 Mk.2 unit. With some proper attention I know I could easily add a minute to the accuracy, but for now it's fun and it's mine.

I don't have the money for an as-new original stock No.4 barrel (~£600+) and I certainly don't have the money to order a custom barrel, bearing in mind the condition of the receiver it's going onto. I'll keep that money for my target rifle!

well done

I found my SMLE #4 propping open a door at a bait shop in Sheboygan Wisconsin (USA). I got to talking with the owner and ended up buying it for $100.-. This was around 1985. It's now a wall hanger, but I have fired it over the years. I often wonder what story it could tell about its journey in getting to that basement bait shop!

In 1963 some of my colleagues in green decided to make shooting blanks on manoeuvers more fun by tying the end of a cleaning rod into the flash suppressors of their M-14's with alumin[i]um wire from a box of C-rations. Full auto, for a while, then the wire broke and the cleaning rod tip got stuck into a tree somewhere. As far as I know, nobody was wounded or killed thereby -- but some got angry after a vehicle accident and apparently managed flesh wounds with pine needles down the bore. The exercise (look up Swift Strike 3) was suspended a day or so to let tempers cool.

6" grouping @200?

Funny sizes?

There are clearly a number of El Reg readers out there who know a great deal about firearms so I wonder if one of them could answer a question that has always puzzled me: why are gun calibres (almost) always such odd sizes?

For example, in this article we're dealing with .303"; why that "odd" 3/1000 of an inch? Wouldn't .3 be just as good - and surely easier to make? I can just about go for .45, but .44? Or .22? Why are standard NATO round 7.62mm or 5.56mm? Wouldn't 7.5mm or evn 8mm and 5.5mm or 6mm be easier to manufacture.

Re: Funny sizes?

Apparently 7mm would be the ultimate calibre. Whenever a group of specialists sit down to work out the best round for a general infantry weapon they come back to 7mm.

But as Ian V Hogg states "nobody ever gets a 7mm round as a result of it!"

Too many vested interests and politics basically.

However, it doesn't really matter. After WW2 they poured over masses of infantry reports and injury details and found that in a combat situation you are more likely to get hit by random flak/shrapnel than a aimed bullet over 50m+ range.

So all that's important is to be able to spray as much random lead down range as possible in the hope that something gets hit or keeps their head down. Hence the move to smaller rounds that are easier to carry but don't have the 2000m+ ranges. If it will still hurt at up to 300m it will do.

Re: Funny sizes?

"Apparently 7mm would be the ultimate calibre. Whenever a group of specialists sit down to work out the best round for a general infantry weapon they come back to 7mm"

<snip>

7 mil rounds have been around for ages, I recall using a Remington 7 mil in the eighties, I also used the French FR F1 which was 7.5, the Belgian FAL and British SLR which were 7.72, the AK 47 7.62 short up to the Stoner 50 mil (12.7 in French) and the lovely FAMAS in 5.56.

As to the other person asking about why Calibers are so strange, it is to do with the conversion twixt metric and non metric so 5.56 comes out as .223. Now a bullet such as a 7.62 (.308)is not actually 7.62, it is generally 7.8 or 7.82 which is as it happens .308. The caliber refers to caliber of the barrel at the start of the rifling and is an internal measurement. It all gets a bit confusing and the US have used some wonderful calibers over the years.

I recently had reason to fire an MP7 which is 4.6 caliber, a Magpul FMG9 (wierd stuff) and by my side I have an automatic pistol which is 7.65 in caliber and preferred weapon to agents who have lots of 0s and a 7 in their name.

Re: Funny sizes?

Really sorry if I'm being even more stupid than usual, but I still don't understand.

I appreciate that the conversion factor could result in some funny sizes in a different set of units, but if you're European (other than British) you work in metric by definition so why would you choose 7.62mm rather than 7mm or 8mm? Similarly, if you're a Brit or a Yank, you probably work in inches so why would you choose .203 or .303?

Re: Funny sizes?

"you probably work in inches so why would you choose .203 or .303?"

If you look up the measurements of a .303 round, you'll note that the round is .54 at the rim, .46 at the base, and .34 just before the crimping to put the (.31) bullet in. The round is 2.2" long in total.

So it does extensively use imperial measurements. .303 seems to have come from measuring the bore size in 1880, which seems to have allowed a 0.01" gap on either side of the barrel, possibly to allow for black powder fouling the rifle. (The .303 originally started with gunpowder as a propellent, before using "smokeless" guncotton and then cordite in British Army use, and pretty much everything imaginable in commercial production since 1880!)

my 2 cents

Truly the only thing I remember/know about 7mm was remembering in the hunter safety class materials how they had just about the longest accidental kill range (ie. shoot up in air randomly) of any major common hunting rifle. Don't remember exactly but want to say it was 5 miles or something ridiculous like that.

Re: Funny sizes?

"I believe technically the EM-2 reached troop testing and got a "proper" service name for a while."

<snip>

It did get there, was tested and found to be a good weapon. The US however decided at the time that 7.62 / 30 Cal was the way to go and that all nations should adopt it.

I used one of the early weapons that derived a lot of its features from the EM2. That weapon was the FAMAS and it was great to fire both on the range and in combat and it was second to none in its day for grenade delivery out to 400 metres (AP) and anti tank (actually vehicle) out to 100 meters.

Have fired various similar weapon (Tavor, AUG) since but none as good as the FAMAS. It has recently got a new life in its role as preferred infantry weapon on the FELIN platform.

Re: Funny sizes?

7.65/.32ACP would be a round that may leave a target shaken but not stirred, the hole at the end of the barrel doesn't look too bad but the crappy little cartridge and it's small load of propellant makes it more dangerous at any appreciable distance if the pistol is thrown rather than fired,

I had a Mauser 1934 hammerless some years ago, reasonably accurate for what it was but what my Great Granddad would have called a dog gun for scaring away the dog packs in India.

Re: Funny sizes?

>So all that's important is to be able to spray as much random lead down range as possible in the hope that something gets hit or keeps their head down.

Often the keeps head down is the most important thing for many roles (not everyone gets to be Rambo). My dad was medievac in Vietnam and if they actually hit enemy soldiers they often had to fly back under fire to pick them up. He did things like use a Thompson machine gun but loaded with a certain percentage of tracer rounds to match that of a M60 firing one every 5 just to keep heads down while they picked up the wounded. He said he was also a real big fan of grenade launcher with smoke.

Re: asdf Re: Funny sizes?

"....My dad was medievac in Vietnam and if they actually hit enemy soldiers they often had to fly back under fire to pick them up.....He said he was also a real big fan of grenade launcher with smoke." They also used to drop a lot of CS tear gas around jungle landing zones as it was 'non-lethal' and therefore did not contravene the Red Cross markings. Around pick-up zones they used more tear gas than napalm as it could also be dropped closer to friendly troops. Of course it wouldn't have made such a good line for the movies - "I love the smell of tear gas in the morning...."

Re: Funny sizes?

Pure speculation on my part - the original vendor lock-in?

In other words, was there a time when the company that supplied the rifles also supplied the ammo? If that was the case, it would not have been in their interests to make the ammo the same size as a competitor's ammo. And once the funny size was widely used, it would tend to self-perpetuate.

It isn't just rifles. Another example is railway track guages. And what about the size of what is now a standard (UK) housebrick?

Edit - I've just realized there's also a battlefield reason for funny sizes. You don't want the opposition using your own ammo against you, if they capture some! So each army using its own size that's different to any potential enemy army at the time that the rifle bore is adopted, makes perfect sense. Even better if the size is sufficiently similar that some stupid soldier tries using captured ammo and blows himself up with it.

Re: Funny sizes?

Oh and on the subject of different sides having different ammo.

Due to the British Army accepting a rimless cartridge for their (British-built) tank and armoured car machine guns (the BESA - an adaption of a Czech design) while still retaining a rimmed .303 for infantry, they could use the German 7.92 ammunition.

And with both sides putting 9mm Parabellum in sub-machine guns and pistols, there was plenty of scope for reuse there.

Re: Funny sizes?

Short story is that many of these calibers were invented over 100 years ago. Heck anything that is .50 or even .456 can arguably be traced back to the old British muskets. There was no sensible reason for making rifles use those calibers (way too big), but the gun inventors were used to it and arguably it gave them some leeway as manufacturing techniques were not as precise as they are now obviously. As for using old rounds like the Russian 7.62? Well they like it and see no reason to change. The Yanks love their .45 despite it being older than anyone alive and don't you dare suggest taking it away from them! So many people use the old calibers, it is just easier to keep using them.

5.56 rounds are a relatively recent invention and were a compromise between the big fat rounds and the smaller sub-machine gun like rounds. It was meant to be a suitable round that everyone could use hence it is known as the standard NATO round. New stuff 5.7, 4.6 etc are the recent attempts by gun makers to make something new, but has not gained a lot of traction.

A few weeks ago an old army officer told me about dodging a .50 round (I reckon it was actually .456) fired at him in Northern Ireland by a chap using a Martini Henry. Google search will tell you this is a Boer war era rifle and actually a predecessor to the Lee Enfield mentioned in the article. Despite being an old relic, the troops were pretty respectful of that round, it was pretty accurate and went a bloody long way down range. Anyway the chap got back circa 400 rounds of .303 courtesy of several GPMGs. The Garda probably had to mop out what was left of him.

any scrap mister!?

i came on here expecting to see a rifle that had been built from old washing machine parts that had been pinched from peoples front gardens by an overly friendly if somewhat intimidating irish man whose preferred method of transport is the Transit Van.............instead i am greeted by what appears to be a completely false NO SCRAP METAL USED WHAT SO EVER article, showing a rifle being built from every piece of correct equipment. i feel cheated.

UK laws

Very happy to see that someone can legally home-build and use a rifle in the UK. As noted in a comment above a lot of the Daily Mail style articles in the press, tv etc give the impression that all potentially dangerous activities must be forbidden rather than regulated.

As for El Reg's headlines - the more extravegant they are the better they are.

Re: Meh.

Congrats on putting one back together ... and dealing with the legalities!

I was taught to shoot a rifle with a No.8, and went on to shoot a No.4 MkII on the 1000 yard range at Bisley ... definitely a fun experience for a youngster.

After I moved to the USA, I was amazed to find that in the mid 1990's, Gov.UK dumped a load of 1955 still-new-in-cosmoline No.4 MkII rifles to buyers in the States ... they were selling for $300 at the time.

That led to a trip back to Birmingham, the old gun district, and the Alfred J. Parker's Armory Works to pick up a classic Twin Zero sight, and to meet the wonderful old Miss Parker.

Don't you El Reg guys think you're being a BIT sensationalist with this article title? I don't see any evidence of this individual being in ANY way a "gun nut" plus you could NEVER describe the Enfield as a "sniper rifle" (it was never made to be such a firearm).

As others have said, someone found an old receiver and built it up into a functioning rifle. If anything, it's an example of imagination and technical competence.

A "gun nut"?

Why is this guy a nut. I only clicked in to find that out. And here we have a rebuilt Enfield. One of the most ordinary firearms in the World. Let's be clear, a top feed, 5 round bolt rifle without so much as a detachable magazine. I mean its got NOTHING that would appeal to an enthusiast except its history. BRITISH history.

What Makes This Guy A Nut?

I think more is being said about the author than about the subject. I think he is afraid of guns. Let me be clearer, I think he is afraid of defending his own safety. Possibly because of the noise. I think it is fortunate I don't have to depend on him, for anything.

Ten round detachable magazine, ordinarily fed with 5 round charger clips. Given, the magazine was attached to early rifles with a small length of chain because the generals of the time had a similar amount of faith in their troops not losing detachable parts than I have in my users, but hey. They stopped doing that on the earlier models about 50 years before this particular one was produced.

@ Frosted Flake

> I think he is afraid of defending his own safety.

I think, to overgeneralise massively, and away from military uses, American gun nuts see guns as tools of defence and personal safety - to be used against large lumps of wildlife and ultimately people if necessary; British gun nuts see guns as tools of sport - to be used against paper targets, inanimate objects and perhaps small furry/flappy creatures.

I've paid more attention to the subject since my son started becoming a bit of a regular at Bisley, and I think the whole attitude divide can be summed up by the fact that, more often than not, on the right-hand side of the pond we shoot at circles, whereas on the left-hand side they shoot at silhouettes.

@AC Re: @ Frosted Flake

> I think he is afraid of defending his own safety.

I think, to overgeneralise massively, and away from military uses, American gun nuts see guns as tools of defence and personal safety - to be used against large lumps of wildlife and ultimately people if necessary; British gun nuts see guns as tools of sport - to be used against paper targets, inanimate objects and perhaps small furry/flappy creatures.

-=-

Now that's just plain wrong.

There are many variations on what constitutes an 'Amerikan' gun nut.

In terms of choice of targets... there happens to be a wider variety of game in the US.

In terms of guns of choice, it depends on where you live. Each state has its own laws concerning what guns a person may own, and what guns can be used for hunting.

You could also classify a gun nut by the number and types of guns owned too.

Re: IMG Re: @AC @ Frosted Flake

".....In terms of choice of targets... there happens to be a wider variety of game in the US....." Indeed. The two sons, both college students, of one of my friends in Louisiana spent their summer working as part-time pest controllers. That didn't entail spraying cockroaches with Raid, but going out on farms and shooting the large numbers of wild pigs that are destroying crops in their area (http://www.bbc.com/news/world-us-canada-29747529). Much more fun than flipping burgers! Ironically, both of them used the same type semi-auto Bushmaster AR-15s as used by Adam Lanza in the Sandy Hook school massacre, which kind of destroys the idea ARs have no purpose other than as 'urban assault rifles'.

I haven't down voted you, but just in case you're getting confused by all your downvotes they are not because Reg readers hate freedom, self-defence or permissive gun ownership rules (though I'm sure some do have their doubts).

They are because you have failed to notice that the title's deliberately hysterical tone is a pastiche of the hysterical articles in the press about the horrors of 3D printed guns.

"Why is this guy a nut. I only clicked in to find that out. And here we have a rebuilt Enfield. One of the most ordinary firearms in the World. Let's be clear, a top feed, 5 round bolt rifle without so much as a detachable magazine. I mean its got NOTHING that would appeal to an enthusiast except its history. BRITISH history"

<snip>

Errrr, no, are you thinking of the US Springfield? The Lee Enfield had five or ten round mags.

Lee Enfield

everybody can argue the virtues of each caliber and their respective country's politics and standpoint on weapons ownership, but the fact of the matter is, the guy did an amazing job restoring a very important piece of history, as well as one beautiful rifle. I'd give my right arm to be able to add one to my collection, but sadly I need that appendage as it holds my trigger finger.

I don't know what the qualifications are to be designated a sniper rifle, but if I recollect, it's generally considered starting at 300 meters and continuing out to almost 2000 m. 0 to 300 meters would be categorized infantry rifle class.

Sure, we can argue details all day long, the fact is the guy did a great job

Re: Scary shit

I've been working on getting my weapons safety officer certification and in my studies I've come to one indisputable conclusion about gun safety: There are no such things as accidents. You either take the proper precautions and respect the fact that any weapon is dangerous if not used properly, carefully or responsibly.

For example, a person accidently shoots themselves while cleaning their weapon - Not accidental. they didn't clear their weapon first.

Accidental discharge due to dropping a loaded weapon - Not accidental Why was a round in the chamber, why didn't they maintain control of the weapon? Why wasn't the safety engaged?

I could cite dozens of examples of irresponsible gun owners and criminals, but there's no need. However, I fail to see why a properly licensed or responsible and qualified adult can't own a weapon.

Calibre refers to the diameter of the projectile (bullet), not length, weight, type or anything else. Sometimes the calibre becomes synonymous with the cartridge but not always. For example .308 is actually .308 winchester and uses a .308 diameter bullet but there are plenty of cartridges that use .308 projectiles eg .30 carbine.

The cartridge is the brass (usually) case in which the propellant is housed and which the projectile is inserted. To add to the confusion the bullet, powder and case once assembled along with the primer are collectively known as a cartridge, bullet or round. Most people use these terms interchangeably.

Anyway back to the point... The story I was told, which makes sense to me at least, is that a lot of the calibres date back to a time when accurate measurement was performed using something little more accurate than a stick. As these calibres evolved from the original low-ish pressure lead ball, which was a bit more tolerant to dimensional differences, to higher pressure jacketed rounds, which really aren't, it became necessary to improve the accuracy of measurement and standardise each calibre.

I have no idea how many "standards" there were/are but the result was/is a selection of common diameter measurements that most cartridges and therefore barrels and projectiles are based off of. If a manufacturer of any of the above wanted to produce a new product (eg a new cartridge) in a new size then it required bullet, barrel and cartridge design whereas using a common calibre allowed them to use off the shelf barrels and bullet heads for their new cartridge.

There were/are exceptions to this. Some more modern projectiles use a new fangled thing called physics to calculate the required parameters for a desired outcome. This results in some fairly weird numbers too. for example the .408 cheytac dates, I think, from the late 90s. Even this though is still caught up a bit in the past as it uses a cartridge case from the older 505 Gibbs.

Then there is the wow factor/bigger is better tendency. This breaks down into three sub-categories

a) Some of the larger cases exist (i believe) purely because a particular number (bigger usually) sounds better. 700 Nitro Express being one of them.

b) Some obscure cartridges were designed purely for a specific purpose, normally military ie body armor defeating (FN 5.7) or a desire to be quieter than usual (300 BLK) but sometimes record breaking (22 Eargesplitten Loudenboomer) - Arguably this falls into the section above I know

So the short answer is

Sometimes it's the legacy of older less accurate measurements being standardised using modern techniques or a change in measuring standard (inch/mm to inner to outer bore)

Sometimes it's the result of research to find the optimal dimensions for a desired end result

I blame the empire!

Because it was large, made things up as it went along and invented the Imperial measurement system to annoy the French. A possible explanation for how various 'calibres' evolved went like this..

Back in the day guns were sized based on projectile weight, so 12-pounder, 17-pounder etc. So weight of shot defined barrel diameter. Then along came muskets and a need to standardise ammunition. So they derived from the gauge system used in shotguns still, ie a 12 gauge has a bore size of 1/12lb of lead formed into a sphere. Some old rifle/pistol calibres then got based on that, or dividing up an ounce of lead.

That kind of fits with tradition, but not sure how plausible it would be. It's a way to standardise calibres or ammunition manufacturing, but by that point in history it have been just as easy to work from measurement or gauges. I still envy our colonial cousin's ability to experiment with wildcat rounds though. Subject to state laws, BATF regs etc etc..

Re: I blame the empire!

Hah. You'd think, but how heavy was a french 36 pounder cannon ball? The answer is 39 pounds, 11 and a half ounces. In generally accepted English pounds before standardisation in 1824 of course. No idea what that is in modern (1876) Imperial, but I'd assume that it's going to be different.

Muskets were actually hand manufactured everywhere to different sets of measurements and it was reasonably common to get your own set of moulds to pour lead into to make bullets for your weapon that would fit. ;)

nomenclature...

a .303 Lee Enfield round, has a larger diameter than a .308 Winchester round:

.303 - Bullet diameter 7.92 mm (0.312 in*)

(Source: http://en.wikipedia.org/wiki/.303_British )

.308 - Bullet diameter 0.308 in (7.8 mm)

(Source: http://en.wikipedia.org/wiki/.308_Winchester )

*others may say 0.311 inch diameter

Calibre (in terms of barrels) is either:

The distance across the diameter of the barrel from the lands to the lands

or

The distance across the barrel from the grooves to the grooves.

- This does vary, "lands" are the innermost part of the barrel's rifling, in between the grooves - and when the diameter is determined on the grooves, then its the outermost part of the barrel's rifling - which is usually a different diameter - i'm not sure how polygonal rifling affects that.....